It has previously been proposed in U.S. Pat. No. 4,515,266 to Myers issued May 7, 1985 to provide a package for preserving produce including a container formed of a high barrier plastic film which is provided with a preservative gas and perforated to provide a gas pressure within the container sufficient to inhibit air flow into the container and to allow gas outflow from the container. In the Myers '266 patent the high barrier plastic film is defined as having a low gas permeability to O.sub.2 of less than 1.0 cc and CO.sub.2 of less than 5.0 cc per mil (0.001 inch) thickness per 100 square inches per 24 hours at standard atmospheric temperature and pressure of 0.degree. C. and 760 mm Hg. Such high barrier plastic film has been found to be unsuitable for packaging cherries commercially in 20 pound packages to preserve them for extended shelf life.
U.S. Patent No. 4,883,674 to Fan issued Nov. 28, 1989 shows a packaging method and package for cut fruit and fruit salad which includes a sealed imperforate container with a high barrier plastic film portion which has an equilibrium protective gas atmosphere within the container of about 2-5% oxygen, 10-15% carbon dioxide and the balance nitrogen. However, this package is not suitable for packaging cherries for preservation to provide an extended shelf life because it produces anaerobic conditions for the cherries causing them to rapidly decay because the protective gas has less than 4% O.sub.2 due to the use of a high barrier film with low gas permeability. The packaging method and package of the present invention overcomes these problems by employing a low barrier plastic film having a high gas permeability and by providing additional perforations in the plastic film to provide the proper gas permeability to avoid anaerobic conditions for cherries. Thus the package of Fan has a permeability of about 4 to 12 cc of oxygen per day per ounce of produce. The low barrier plastic film employed in the package of the present invention has a gas permeability of at least 80 cc of O.sub.2 and 490 cc of CO.sub.2 per mil (0.001 inch) of thickness per 100 square inches of area per day at 25.degree. C. temperature and 760 mm Hg pressure, and for low barrier, high density polyethylene preferably has a permeability of about 400 cc O.sub.2 and 1164 cc of CO.sub.2 per mil thickness per 100 square inches per day at 25.degree. C. and 760 mm Hg.
More recently U.S. Pat. No. 4,943,440 to Armstrong issued Jul. 24, 1990 discloses a packaging method and package for packaging cut vegetable salad including a sealed imperforate container having a controlled atmosphere of 0.8-1.5% oxygen and 8-12% carbon dioxide with the balance being nitrogen. However this package is not suitable for packaging cherries because the oxygen percentage is too low resulting in anaerobic conditions and the container is made of high barrier plastic film having a gas permeability of about 18 to 22 cc oxygen per 24 hours per ounce of produce. While this sealed imperforate container may be provided with a cover portion of low barrier plastic film having an oxygen permeability in the range of 200 to 500 cc per mil thickness per 100 square inches area per day, there are no apertures provided the film. This results in the extremely low oxygen content modified atmosphere of 0.8-1.5% oxygen which is insufficient for packaging cherries because it results in an anaerobic condition. Thus, in accordance with the present invention it has been found that a residual preservative gas of higher oxygen content containing about 4-14% oxygen and 4-13% carbon dioxide is necessary for satisfactorily packaging cherries to provide a long shelf life.
Another relevant patent is U.S. Pat. No. 4,224,347 to Woodruff issued Sep. 23, 1980 which shows a packaging process and package for extending the shelf life of cut vegetables employing an imperforate container of plastic material which may be low barrier plastic film having a permeability to oxygen of at least about 500 cc per 100 square inches per 24 hours per mil and a permeability to carbon dioxide of at least 1350 cc per 100 square inches per mil. However the modified atmosphere within the package is provided with at least 25% oxygen and about 3% carbon monoxide and a maximum of 20% carbon dioxide. This atmosphere is unsuitable for packaging cherries because it causes decay and degrades their taste due to its high oxygen and high carbon dioxide content. Thus it has been found that for preserving cherries it is necessary to provide the preservative gas within the container with an oxygen content percentage much less than that in air or less than the approximately 21% oxygen content of air. Preferably the preservative gas should have an oxygen content of about 4-14% by volume.
It is old to provide perforations in plastic packages to change the permeability thereof as discussed in the article "Controlling Atmosphere in a Fresh-Fruit Package" by P. Veeraju and M. Karel, Vol. 40, No. 2, published in 1966 in the periodical Modern Packaging. While this article also discusses employing low barrier plastic films for packaging, it does not suggest a residual preservative gas atmosphere within the package containing 4-14% oxygen and 4-13% carbon dioxide as measured approximately one week after sealing in accordance with the packaging method of the present invention. Also there is no indication that air should be partially evacuated from the package and refilled with an injection gas containing a high percentage of carbon dioxide in the range of 30-50% dioxide with the balance nitrogen when one half the air is removed as in the present invention. It has been found that in the package of the present invention most of this initially high percentage of carbon dioxide is quickly absorbed into the cherries to reduce the respiration rate of the cherries. Thus in one embodiment the respiration rate of the cherries after packaging reduced to about 25% of its respiration rate immediately prior to packaging. This rapid reduction in respiration rate of cherries due to the absorption of carbon dioxide into the fruit greatly increases shelf life and is not recognized in the prior art including the article by Veeraju and Karel.
U.S. Pat. No. 4,548,852 to Mitchell issued Oct. 22, 1985 and U.S. Pat. No. 4,548,824 to Mitchell et al. issued Oct. 22, 1985 both show that it is old to provide a package of meat or vegetable products for home freezing by providing a rigid plastic tray with a flexible plastic cover which collapses in order to provide the maximum expulsion of air from the package prior to freezing. The package is provided with a replaceable seal covering a hole in the package cover to accomplish this evacuation. However they do not disclose a package for preserving cherries provided by a container having at least a portion thereof made of low barrier plastic film containing a residual preservative gas mixture including oxygen at a percent less than air and carbon dioxide at a percentage greater than air in the manner Of the present invention. Instead the oxygen is provided at a higher percentage concentration than that in air, such as 70% O.sub.2 for meat, and in this regard is similar to the above-discussed Woodruff '347 patent.
U.S. Pat. No. 3,630,759 to Rumberger issued Dec. 28, 1971 discloses a method of packaging plant foods within an inner plastic pouch and an outer plastic pouch having a gaseous atmosphere therebetween having an oxygen content less than about 15% by volume. However this packaging is more complicated than that of the present invention in that it requires the use of two bags and maintaining a preservative atmosphere between the walls of the two bags which is impractical.
Another patent of interest is U.S. Pat. No. 4,055,931 to Myers issued Nov. 1, 1977 which is directed to a method of providing a controlled atmosphere around a perishable product enclosed within a flexible bag by evacuating the bag and then injecting a controlled atmosphere into the bag for preserving agricultural products such as strawberries and tomatoes. The final atmosphere within the bag does not contain oxygen but apparently consists entirely of carbon dioxide and nitrogen which is unsuitable for the preservation of cherries since it produces anaerobic conditions. Also this has a disadvantage of requiring an air-tight flexible bag which, of course, means that the bag must be made of high barrier plastic material.